The present invention relates to a field harvest cooling system that cools the plants or plant products and maintains a blanket of chilled gas around the plants or plant products to slow degradation caused by respiration and/or transpiration. As used herein, the term "plants and plant products" is intended to cover all edible and non-edible plants that are eaten or used in their entirety (e.g. celery and tobacco, respectively) or where only a portion of the plant is eaten or used (e.g. tomatoes and seeds which produce edible or inedible oils). For the sake of brevity, all future reference herein will be made to plants. It should be understood, however, that the term "plants" also covers plant products whether edible or inedible.
Immediately following harvest in the field, plants such as fruits and vegetables, and non-edible plants such as tobacco begin the process of respiration. Respiration is generally expressed by the simplified process formula shown below. EQU C.sub.6 H.sub.12 O.sub.6 +6O.sub.2 .fwdarw.6CO.sub.2 +6H.sub.2 O+heat energy
In the respiration reaction a sugar, such as glucose or fructose, combines with oxygen to yield carbon dioxide, water and energy in the form of heat. The production of heat is principally responsible for the degradation of the harvested plants by (a) fueling the continuation of respiration and (b) triggering water loss (transpiration) which results in reduced product weight and diminished quality through over-ripening, fermentation and spoilage.
The heat energy produced during respiration is transferred to the plants resulting in an increase in temperature. For some plants, particularly those having a relatively high sugar content, respiration can result in spoilage within just four hours from the time of harvest.
In a typical harvesting operation, a harvester uses a picker or combine to remove the plants from the field or the plant products from the field plants. The picker/combine will have some limited integral storage area. When this storage device is filled, the picker/combine will unload the plants into a transport truck or bulk shipping container. When a truck is filled with plants or shipping containers containing the plants, the truck departs the field site for a final processing site or storage area.
Thus, significant time is lost from the moment of harvest until the transport truck departs the field site. Accordingly, the distance the transport truck may travel before the onset of spoilage is limited and determines how far from the field of harvest the plants may be processed.
In order to avoid excessive spoilage of harvested plants, it has been necessary to operate within the maximum allowable transport time measured from the field to the processing site and then to ensure that all plants delivered to the processing site are harvested within the maximum allowable transport time. One method of extending the maximum allowable transport time is to harvest when outside temperatures are relatively low such as during cool harvest seasons and/or early in the morning.
Harvesting under reduced temperature conditions to slow the respiration reaction can also be accomplished by treating the harvested plants with chilled water or ice. Such methods, however, are disadvantageous because they are costly, cumbersome and often times difficult to carry out because water and power sources may not be readily available in the field. In addition, there is a potential problem of waste-water disposal which may add to the cost of the harvesting operation.
It would therefore be a significant advance in the art of harvesting and transporting plants to a processing site if the harvested plants could be immediately and efficiently cooled and transported under reduced temperature conditions from the harvest site to the processing site.